Means and method of amplifying electric wave energy



Jan. 28, 1941.

MEANS AND METHOD OF AMPLIFYING ELECTRIC WAVE ENERGY 7 Filed March 1'7,1958 an 10 -|Fo C 26 g I 15 15 {RM FFiIIIIIIiI Ftgui *Il w J8 INVENTOR.

K. RATH 2,229,705 I Patented Jan. 28, 1941 UNITED STATES MEAN S ANDMETHOD OF AIVIPLIFYING ELECTRIC WAVE ENERGY Karl Bath, New York, N. Y.,assignor to Radio Patents Corporation, New York, N. Y., a corporation ofNew York Application March 11, 1938, s ri l No. 196,394

v 8 Claims.

The present invention relates to electric frequency discriminatingsystems or networks and methods of operating the same for use asfilters, compensating or equalizing circuits, tone control, and otherpurposes well known.

More particularly the invention is concerned with systems or networks ofthe above character comprising one or more amplifiers such as electrondischarge valves employing inverse or negative feedback or signaldegeneration for selected predetermined frequencies or ranges offrequencies in such a manner as to obtain a desired resultant frequencyresponse characteristic of the amplifier or associate circuit connectedtherewith.

Accordingly, an object of the invention is to obtain a desired frequencyresponse characteristic of a single amplifier stage by use of inverse ornegative feedback.

Another object is .to obtain a desired frequency response characteristicof a single amplifier stage normally having a broad frequency responseby utilizing selective inverse or negative feedback.

Still a further object is the provision of an amplifier withintercoupling input and output elements normally producing asubstantially broad frequency response and means for modifying theresponse characteristic of the amplifier by selective inverse ornegative feedback to obtain a resultant response characteristic of anydesired shape.

The above and further objects and advantages of the invention willbecome more apparent from the following detailed description taken withreference to the accompanying drawing forming part of this specificationand wherein;

Figures 1, 3, 5, 6, and 7 show single electron valve amplifier stagesembodying selective inverse feedback according to the invention.

Figures 2, 4 and 8 show frequency response curves explanatory of thefunction and operation of the circuits according to Figures 1, 3 and 7respectively.

Like reference characters identify like elements throughout thedifferent views of the drawing.

With the above objects in view, the invention in its general aspectcontemplates the provision of a common return impedance for the grid andanode circuits of an amplifying valve to normally provide a degenerativeor inverse feedback for the current or potential variations impressedupon the input circuit of the valve, and frequency discriminatingelements or networks connected to said common impedance on the one handand to one or more points in either the input or output circuit of thevalve on the other hand thereby to suppress or reduce the effect of"inverse feedback for predetermined frequenciesor ranges of frequenciesand resulting in an amplification and passing of these frequencies tothe outpu circuit in such a manner as to obtain a desired E resultantinput-output frequency response characteristic of the amplifier of anydesired shape to suit any existing requirements.

The advantages of inverse feedback such as high operational stability,freedom from inter-1 ll) e e low n ise level, indep nd nce o l echaracteristics, etc., are well known. In the prior art systemsemploying negative or inverse feedback, these advantages could not befully realized without material loss of amplification due to the factthat all frequencies passed by the amplifier were subjected to theinverse feedback action; thereforeto obtain any amplification the degreeof feedback had to be limited to prevent the loss of amplificationcaused thereby. By the improvements according to the present invention,a high degree of inverse feedback or degeneration is employed for allfrequencies to which the amplifier is normally responsive and only thedesired frequencies are by-passed around the inverse feedback impedanceresulting in increased stability and efficiency and other desirableadvantages.

Referring to Figure 1 of the drawing which shows a singleresistance-coupled amplifier stage 39 employing inverse or negativefeedback accord-. ing to the invention, item 10 represents an amplifyingvalve of standard construction in the example shown comprising a cathodel I which may be a directly or indirectly heated cathode, a grid I2 andan anode or plate l3. The anode is con-v nected to the cathode through aload impedance, in the example shown, a resistance M in series with asource of high potential for supplying the anode current of the valvesuch as battery [5 40 shunted by a by-pass condenser l5 and a commoncathode return or negative feedback impedance, in the example shown, aresistance 16. Item I! is a coupling condenser connected between theanode and the output terminal c, -th e v other output terminal 41 beingconnected to the lower grounded end (ground l8) of the inverse ordegenerative feedback resistance I61 Input wave energy which may be ofaudio, intermediate or high frequency is impressed upon an input 59impedance such as resistance l9 across the input terminals a.-b. Theimpedance l9 has its upper terminal connected to the grid 12 and its weterminal to the wer o sround endor the resistance 15 throug a p ur li yof enqenser is 20 arranged in series. The junction points between thecondensers 20 are connected through impedances such as resistanceelements 2| in the example shown to the cathode, while the lowerterminal of the input impedance I9 is connected to the cathode throughan additional resistance 2|. There is further provided in the exampleshown a} resistance 22 connected between the upper terminal of thefeedback resistance I 6 and the cathode shunted by a by-pass condenser23 to provide proper operating grid biasing potential for the valve in amanner well understood. In an arrangement of this type the condensers 20and resistance elements 2| form a high-pass filter connected across thecommon return or inverse feedback resistance IE on the one hand andterminated by the resistance 2| on the other hand which latter ispreferably of the same value as the resistance It. As a result, theamplified high frequency components of an input signal Wave across thecommon return resistance IE will be passed by the high pass filter andproduce across the terminating resistance 2| voltage variationscorresponding to these frequencies Which voltages being applied inseries with the grid circuit will oppose the input signal wave voltagesof the same frequency which will therefore become degeneratedby thisinverse feedback. The amplified lower frequency components however willbe passed directly to the cathode or upper terminal of the inversefeedback resistance [6 and will therefore not be degenerated resultingin these lower frequency components to be amplified and transmitted tothe output circuit connected to terminals cd.

In Figure 2 there is shown a frequency response curve of an amplifieraccording to Figure 1. Curve A represents the frequency response (outputcurrent or potential across c--d in suitable units such as 'db. units asa function of the frequency f of the input potential impressed upon ab)of the amplifier without the inverse feedback arrangement which ischaracteristic of a resistance coupled amplifier as shown and comprisesa broad band of operating frequencies. Curve B shows the responsecharacteristic with the inverse feedback system embodied in theamplifier as described and resulting in a low pass efiect with a cut-offfrequency shown at in. In order to improve the sharpness of this cutoffin Figure 1, induction coils may be provided in place of the resistances2| or of both the resistances 2| as well as the resistances l6 and 2|.It is further understood that any other type of amplifying valve such asa screen grid or pentode valve may be provided in place of a threeelement valve shown for illustration. Furthermore, it is understood thatin place of a battery as an anode potential source, the space currentfor the tube may be supplied from a potentiometer'or a batteryeliminator in common use in amplifier systems.

Referring to Figure 3 there is shown a system similar to Figure 1wherein the filter associated with the inverse feedback resistance l6 isof the low pass type comprising resistance elements 2| serially insertedin the grid circuit in series with a further condenser 24 of largecapacity and condensers 20 connected between the junction points of theresistance elements 2| and the cathode or upper terminal of the inversefeedback resistance 6. In this-manneran inverse response curve, i. e. acurve of the high-pass type, 'is obtained by an arrangement according 75to Figure 3. This is shown by curve C in Figure 4, other details beingsubstantially similar to the previously described circuit.

Referring to Figure 5, this is substantially similar to Figure 1 anddiffers therefrom merely by the fact that the resistance elements 2| areconnected to different taps on the inverse feeds back resistance Hi. Theresponse characteristic of this circuit'is substantially similar to thecharacteristic of the circuit of Figure 1 and shown in Figure 2.

Referring to Figure 6, this shows a circuit of the type according toFigure 3 and differs from the latter by the connection of the condensers20 to variable taps of the cathode return or inverse feedback resistanceHi. The function and operation of this circuit is substantially similarto the circuit of Figure 3 and the response characteristic obtained isof substantially the same type as shown in Figure 4.

Referring to Figure 7, there is shown a further modification of a systemaccording to the invention wherein a plurality of condensers 26 areconnected between the cathode and different taps on the output or loadresistance l4 thereby forming a low pass filter in the output circuit.There is further shown in Figure 7 the connection of the input terminalb to a point of positive potential of the anode source l5 to compensatefor excessive steady or quiescent operating grid bias produced by thevoltage drop through the inverse feedback resistance 6 to obtain a mostfavorable operating point on the valve characteristic. The tapped offportion of the source I5 is by-passed by a condenser l5".

In Figure 8 there is shown the frequency response curve for the circuitaccording to Figure 7. Curve A shows the response curve for theamplifier without the feedback arrangement. which corresponds to thecurve characteristic of a resistance coupled amplifier. Curve D is thecharacteristic of the filter I4, 26 per se and curve E the resultantinput-output response characteristic of the amplifier.

It will be evident from the above that the invention is not limited tothe specific circuit arrangements and methods described for illustration but that the novel concept and principle of the invention aresusceptible of numerous variations and modifications coming within the]broader scope and spirit of the invention as defined in the appendedclaims. The specification and drawing are accordingly to be regarded inan illustrative rather than in a limited sense. I I claim:

1. In a translation system for electric wave energy, an amplifying tubecomprising a cathode, an anode and at least one control grid, couplingimpedance means connected between the alternating potential referencepoint of the system and said grid and anode, respectively, adegenerative impedance connected between the cathode and the alternatingpotential reference point, said degenerative impedance being designed topresent substantially equal impedance to all frequency components of theenergy to be translated, and means to provide a plurality of circuitpaths having different frequency discriminating characteristics betweendifferent points of said degenerative impedance and at least one pointof one of said coupling impedance means, thereby to cause varyingportions of said degenerative impedance to form a common effectivecathode return path for said input and output impedance means forcomponents of different frequency of the energy being translated.

2. In a translation system for electric wave energy, an amplifying tubecomprising a cathode, an anode and at least one control grid, inputimpedance means having its high potential side connected to said grid,output circuit impedance means connected to said anode, a degenerativeresistance connected between the cathode and the alternating potentialreference point of said system, and means to provide a plurality ofcircuit paths having different frequency discriminating characteristicsconnected between the low potential side of said input impedance meansand different points of said degenerative resistance, thereby to causevarying portions of said degenerative resistance to form an effectivecommon cathode return path of said input and output impedance means forcomponents of different frequency of the energy being translated.

3. In a translation system for electric wave energy, an amplifying tubecomprising a cathode, an anode and at least one control grid, an inputcircuit connected to said grid, a first output impedance connected tosaid anode, a second degenerative impedance connected between thecathode and the alternating potential reference point of the system,said degenerative imedance being effective in normally substantiallyequally reducing the amplifying gain for all frequency components of theenergy being translated, and means to provide a plurality of circuitpaths having difierent frequency discriminating characteristicsconnected between at least one point of said impedances and differentpoints of the other impedance, thereby to cause varying portions of saiddegenerative impedance to form an effective common cathode return pathfor said input and output impedance means for components of differentfrequency of the energy being translated.

4. In a translation system for electric wave energy, an amplifying tubecomprising a cathode, an anode and at least one control grid, inputimpedance means having its high potential side operatively connected tosaid grid, output impedance means connected to said anode, adegenerative resistance connected between the cathode and thealternating potential reference point of said system, a furtherimpedance connected between the low potential side of said inputimpedance and the cathode, and a frequency discriminating networkcomprising series and parallel impedance elements having differentimpedance characteristics dependent upon frequency, said series elementsbeing connected between the low potential side of the input impedanceand a point of said degenerative resistance relatively remote from thecathode, and said parallel elements being each connected between ajunction point of said series elements and a point of said degenerativeresistance relatively close to the cathode, thereby to cause varyingportions of said degenerative resistance to form an effective commonreturn path for said input and output impedance means for high and lowfrequency components, respectively, of the energy being translated.

5. In a translation system for electric wave energy, an amplifying tubecomprising a cathode, an anode and at least one control grid, inputimpedance means having its high potential side operatively connected tosaid grid, an output circuit connected to said anode, a degenerativeresistance connected between the cathode and the alternating potentialreference point of said system, a further impedance connected betweenthe low potential side of said input impedance means and the cathode,and a frequency discriminating network comprising a plurality ofcapacity elements in series connected between the low potential side ofsaid input impedance means and said reference point, and a plurality ofresistance elements each connected between a junction point of saidcapacity elements and a point of said degenerative resistance remotefrom said zero reference point.

6. In a translation system for electric wave energy, an amplifying tubecomprising a cathode, an anode and at least one control grid, inputimpedance means having its high potential side operatively connected tosaid grid, an output circuit connected to said anode, a degenerativeresistance connected between the cathode and the alternating potentialreference point of the system, a further impedance connected between thelow potential side of said input impedance means and the cathode, and afrequency discriminating network comprising a plurality of seriesresistances connected between the low potential side of said inputimpedance means and said reference point, and a plurality of capacityelements, each connected between one junction point of said resistanceelements and a point of said degenerative resistance remote from saidreference point.

7. In a translation system for electric wave energy, an amplifying tubecomprising a cathode, an anode and at least one control grid, inputimpedance means having its high potential side operatively connected tosaid grid, an output circuit .connected to said anode, a degenerativeresistance connected between the cathode and the alternating potentialreference point of said system, a further resistance connected betweenthe low potential side of said input impedance means and the cathode,and a frequency discriminating network comprising a plurality ofcapacity elements in series connected between the low potential side ofsaid input impedance means and said reference point, and a plurality ofresistance elements each connected between a junction point of saidcapacity elements and the cathode.

8. In a translation system for electric wave energy, an amplifying tubecomprising a cathode, an anode and at least one control grid, inputimpedance means having its high potential side operatively connected tosaid grid, an output circuit connected to said anode, a degenerativeresistance connected between the cathode and the alternating potentialreference point of the system, a further resistance connected betweenthe low potential side of said input impedance means and the cathode,and a frequency discriminating network comprising a plurality of seriesresistance elements connected between the low potential side of saidinput impedance means and said reference point, and a plurality ofcapacity elements each connected between one junction point of saidresistance elements and the cathode.

KARL RA'I'H.

